1. Field of the Invention
The present invention relates generally to the making of shaped bodies from formable composition mixes. More particularly, the invention involves the extrusion of compositions comprised primarily of inorganic compounds to produce filamentary bodies having a generally continuous and uniform configuration.
2. Description of the Prior Art
The forming of shaped bodies from compositions comprising essentially inorganic constituents has been well documented by the prior art. Of particular interest in this area of technology is the utilization of compositions that include a metallic compound which is reducible to its free metal state. This permits the shaping of the composition into the desired configuration of the final product, and thereafter reducing and sintering the shaped body to produce a metal article which only requires a minimum amount of final working or finishing. By contrast, the conventional practice of manufacturing metal articles requires the casting of molten metal either into molds of desired shapes or into ingot molds for subsequent mechanical deformation into the final desired shape. In addition to economic considerations of labor and equipment, the production of metallic articles by casting is limited both in the shapes obtainable and the mechanical properties of the cast article. These factors are especially significant in the production of metallic articles having a continuous or filamentary configuration, such as fine metal fibers, wire strands, thin metal ribbons and the like.
A system for making high density filamentary metal articles by utilizing a formable composition mix comprised primarily of inorganic constituents is disclosed by the McIntire et al U.S. Pat. No. 3,671,228. This patent discloses the making of metallic bodies from reducible metal compounds by forming agglomerates thereof by mixing fine particles of the compounds with the plasticizer or binder. The agglomerates are then compacted into the desired shapes, such as extrusion to from continuous strands or the like, and thereafter subjected to a reducing environment. The resulting free metal body is then sintered into a very dense metal product. By mixing metallic compounds of different metals in forming the compacted agglomerates, it is possible through the practice of this technique to produce sintered alloy articles for various applications. The forming compositions or agglomerates utilized by the system of this patent are necessarily of high viscosity in order to accommodate the shaping of same through molding, extruding or similar known forming techniques.
The prior art has also recognized that filamentary bodies in the form of fibers may be made by spinning or extruding compositions that are essentially ceramic or refractory particles dispersed within a carrier to define a sol or slip. Such fibers are subjected to heat treatment for the purpose of establishing a bonded refractory product, such as crystalline fibers. This technique is particularly useful for making alumina fibers or filaments and is well documented by the disclosures of the Blaze U.S. Pat. No. 3,322,865, Winter et al U.S. Pat. No. 3,846,527, Winter et al U.S. Pat. No. 4,010,233 and Pearson et al U.S. Pat. No. 4,071,594. A particular problem encountered in the production of inorganic fibers according to techniques and compositions such as disclosed by these patents is that of imparting the desired physical characteristics to the composition mix in order to accommodate forming the fibers by established techniques, such as spinning and extruding. The Winter et al U.S. Pat. No. 3,846,527 teaches that the spinnability of its composition is achieved by inclusion of a linear polymeric substance, such as a polyacrylamide. The Pearson et al U.S. Pat. No. 4,071,594 is similar in that its composition comprises primarily alumina suspended in a finely divided state with a high molecular weight linear chain polyethylene oxide polymer in an organic solvent.
Prior art techniques for forming filamentary shapes also include extruding polymer or molten metal through an orifice for collection below the extrusion orifice. For example, the Pond U.S. Pat. No. 3,602,291 discloses that discrete metal filaments may be made by extruding a stream of molten metal downwardly through a vertical tube which terminates at its lower end in a quench bath. This technique is similar to the well known procedure of forming powder or shot, but differs therefrom in that the extruded molten metal falls under the force of gravity in a continuous stream or filament and does not separate into discrete filaments until it reaches the quench bath. The Economy et al U.S. Pat. No. 3,723,588 is broadly similar in that a supply of thermoplastic material is extruded through an orifice disposed at the bottom of a vessel to form a continuous filament or fiber that is drawn downwardly and collected on a rotating spool. The polymer cools and solidifies into the fiber through contact with the atmosphere as it is being drawn downwardly and collected. The rate at which the filament is drawn is controlled by regulating the speed of rotation of the collection spool. This system is only an example of other similar known techniques for making synthetic polymer filaments, such as the melt spinning process for Nylon and similar materials which involve extruding through an orifice and then stretching to final size.